The present invention relates to an electric steering wheel lock device for switching a steering wheel of a vehicle between a lock state and an unlocked state to prevent the vehicle from being stolen, and a motor damping structure suitable for use in such an electric steering wheel lock device.
In recent years, vehicles, such as a four-wheel automobile, are equipped with a steering wheel lock device that moves a lock bar from an unlock position to a lock position to lock the steering wheel (steering shaft) and prevent theft of the vehicle.
There are mechanical type and electric type steering wheel lock devices. In a mechanical type steering lock device, a mechanical key is inserted into a key cylinder, which is located near the steering wheel, and turned to lock the steering wheel. In an electric type steering lock device, an electric drive source (actuator) reciprocates a lock bar relative to the steering shaft to fit the lock bar fit to the steering shaft and lock the steering wheel.
Japanese Laid-Open Patent Publication No. 2008-137644 describes an electric steering wheel lock device of the prior art. In this electric steering wheel lock device, an electric motor (DC motor), which serves as a drive source, transmits drive power to the lock bar through a gear mechanism to reciprocate the lock bar.
The electric steering wheel lock device includes a case member formed by a lid (lid member), which serves as a motor holding member for holding the electric motor, and a case body, to which the lid is attached, for accommodating the electric motor, the lock bar, and the gear mechanism. The case member (case body) is fixed by a bracket to a cylindrical column tube that surrounds the steering shaft.
In the prior art, the lid and the case body are die casted from magnesium (cast metal). However, highly rigid resin material is nowadays more used to form the lid and case body due to the recent trend for manufacturing light-weight vehicles.
In the electric steering wheel lock device of the above publication, when the electric motor is operated to lock or unlock the steering wheel, vibration generated by the electric motor is transmitted to the case member, the column tube, and the like through the lid. This generates noise and disturbs the silentness in the passenger compartment.
Japanese Laid-Open Patent Publication No. 2008-168863 (see FIG. 1) describes a technique for reducing the transmission of vibration from an electric motor. The publication describes a non-woven fabric adhered around the casing of an electric motor. The electric motor is pressed into and fixed to a motor fastening portion, which is arranged in the lid, together with the non-woven fabric.
In this technique, however, the non-woven fabric is discrete from the lid, which holds the electric motor. This results in an increase in the number of parts, which contradicts the demand for fewer parts in an automobile.
Japanese Laid-Open Utility Model Publication No. 7-40290 describes a vibration damping technique. This technique is not used for an electric steering wheel lock device but used for an electric retractable door mirror device. The publication describes (FIG. 1, paragraph 0021) a mirror retracting electric motor 10 is held by two elastic arms 44 arranged facing toward each other on a plate 41, which is formed by an elastic member. Vibration generated when driving the electric motor 10 is absorbed by the elastic arms 44. The plate 41 is formed from polyacetal resin, rubber, or the like and is thereby elastic.
The upper side of a casing for the electric motor 10 is clamped by the elastic arms 44. Furthermore, engagement tabs 45 arranged at the distal ends of the elastic arms 44 are engage with the corners of the electric motor 10. This holds the electric motor 10 on the plate 41.
Japanese Laid-Open Utility Model Publication No. 7-40290 describes the absorption of vibration in the direction of the rotation shaft of the electric motor 10 to suppress transmission of vibration to a unit bracket 5 through the plate 41.
However, as discussed in Japanese Laid-Open Utility Model Publication No. 7-40290 (FIG. 1 and paragraph 0021), the effect of suppressing transmission of vibration is assumed to be mainly obtained by an urethane cushion 49 arranged between the electric motor 10 and the plate 41.
Therefore, the cushion 49 increases the number of parts even if the technique described in publication is applied to the electric steering wheel lock device. Furthermore, the lid of the electric steering wheel lock device corresponding to the elastic arms 44 is formed from a die-cast product or highly rigid resin material as described above. In addition, the lid comes into planar contact with the electric motor 10 and the elastic arms 44. Thus, with the technique of Japanese Laid-Open Utility Model Publication No. 7-40290, it is rather difficult to sufficiently suppress the transmission of vibration.